ML20156A241
| ML20156A241 | |
| Person / Time | |
|---|---|
| Site: | Harris  |
| Issue date: | 06/04/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1989-001-02 | |
| Download: ML20156A241 (5) | |
Text
B-355 ACCIDENT SEQUENCE PRECURSOR PROGRAM EVENT ANALYSIS LER No:
Event
Description:
Date of Event:
Plant:
400/89-001 R2 Reactor trip and loss of one train of auxiliary feedwater January 16, 1989 Shearon Harris Summary A turbine trip on low main condenser vacuum was initiated at Shearon Harris when a technician inadvertently opened a valve that vented the main condenser to atmosphere.
The reactor tripped immediately following the turbine trip, and a steam generator (SG) low-low level during the subsequent transient initiated the auxiliary feedwater (AFW) system. The turbine-driven AFW pump tripped off 15 s after it had started. The conditional core damage probability estimated for this event is 1.3 x 10O5. The relative significance of this event compared with other postulated events at Shearon Harris is shown below.
LER 400/89-001 IE-7 1-1E51E-4 1E-3 1E-I j
L360 h EP Trip]
I O
+
36Oh AFW L
K MT AFW LOOP I.precursor cutoff Event. Description On January 16, 1989, Shearon Harris was operating at 100% of rated power when a technician opened an auxiliary steam condensate tank vent valve and established a vent path for the main condenser to the atmosphere. This manually operated valve had been closed to isolate a motor-operated valve (MOV) that had been worked on, and the technician was restoring the system lineup. However, the MOV was not fully closed, and, as a result, vacuum started decreasing in the main condenser when he opened the manual valve. The operators tried, without success, to stop the loss of vacuum by
B-356 reducing the turbine load, and approximately 8 min later, the turbine tripped on low vacuum. The reactor tripped immediately thereafter because of the turbine trip. An SG low-low level during the subsequent transient initiated AFW, and all three AFW pumps started. The turbine-driven AFW pump tripped off 15 s after it had started. This was initially believed to be caused by excessive moisture in the steam supply lines, but it was later concluded that the pump trip was caused by an overspeed signal from the turbine tachometer (see LER 400/89-017). The motor-driven AFW pumps were unaffected and continued supplying water to the steam generators.
Additional Event-Related Information Shearon Harris' AFW system consists of two motor-driven pumps and one turbine-driven pump. All three pumps share a common suction from the condensate storage tank (CST). AFW supplies the three SGs through separate lines (one for each SG), and any of the AFW pumps can supply the SGs.
ASP Modeling Assumptions and Approach This event has been modeled as a loss of feedwater (due to the unavailability of the main condenser) with a failed turbine-driven AEW pump.
Analysis Results The conditional probability of severe core damage for this event is 1.3 x 10-5. The dominant sequences for this event involve unavailability of secondary-side cooling and failure to initiateý feed and bleed. The dominant sequence is highlighted on the following event tree.
Note that two other events occurred at this plant that involved a trip with one AFW pump unavailable (see LERs 400/89- 006 and -017).
B-357 TRANS I T
IAW IMFW I PO SIPRVI HPI HPR PORV STKF CHAL RESEATI I
I EN SEO END NO STATE OK OK CD 12 C
OK OK OK 1 3 CD 14 C
OK OK 15 CD (1) 16 CD 17 CD is ATWS (1) OK for Class D Dominant core damage sequence for LER 400189-001
B-358 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
400/89-001 Event
Description:
Reactor trip and failure of turbine-driven AFW pump to run Event Date:
01/16/89 Plant:
Harris 1 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS
- 1. 0E+00 SEQUENCE CONDITIONAL PROBABILITY SUNS End State/Initiator Probability CD TRANS 1.3E-05 Total 1.3SE-05 ATWS TRANS 3.4E-05 Total 3.4E-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
15 trans -rt AFW MFN -hpl(f/b) -hpr/-hpi porv.open CD 6.1E-06 2.6E-01 17 trans -rt AFW NFN hpi(f/b)
CD 6.1E-06 2.2E-01 18 trans rt AIMS 3.4E-05 1.2E-01 non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
15 trans -rt AFW MFM -hpi(f/b) -hpr/-hpi porv.open CD S.lE-06 2.6E-01 17 trans -rt AFW MFW hpl(f/b)
CD 6.lE-06 2.2E-01 18 trans rt ATWS 3.4E-05 1.2E-01 non-recovery credit for edited case SEQUENCE MODEL:
c:\\asp\\1989\\pwrbseal.cmp BRANCH MODEL:
c:\\asp\\1989\\harris.s11 PROBABILITY FILE:
,c:\\asp\\1989\\pwrý_bsll.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans 5.5E-04 1.OE+00 loop 1.6E-05 5.3E-01 loca 2.4E-06 4.3SE-01 rt 2.8E-04 1.2E-01 rt/loop 0.OE+00 1.OE+00 emerg.power 2.9E-03 8.OE-Ol AFW 3.8E-04 >2.3E-03 2.6E-01 Branch Model:
l.OF.3+aer Train 1 Cond Prob:
2.OE-02 Train 2 Cond Prob:
1.OE-01 Train 3 Cond Prob:
5.OE-02 > Failed Event Identifier: 400/89-001
B-359 Serial Component Prob:
afwfamerg.power 14FW Branch Model:
l.OF.l+opr Train 1 Cond Prob:
porv.or.srv.chall porv.or.srv. reseat porv.or. srv. reseat/emerg.power seal.loca, ep. rec (si) ep.rec tipi tipi (f/b) hpr/-hpi porv.open
- branch model file
- forced Minarick 06-13-1990 12: 58: 09 2.8 E-04 5.0 E-02 1.OE+00 > 1.OE+00 l.0E+00
- 4. 0E-02 2.OE-02 2.OE-02 2.7E-01 5.7E-01 7.0 E-02 3.0 E-04 3.OE-04
- 1. 5E-04
- 1. OE-02 3.4E-01 7.OE-02 > 1.OE+00
- 1. OE+00 1.1E-02 1.OE+00 1.OE+00 l.OE+O0 1.OE+00 8.4E-01 8.4E-01
- 1. OE+00
- 1. OE+00 l.OE-03 1.OE-02 1.OE-03 4.OE-04 Event Identifier: 400/89-001